Anatomic Tissue Layers of the Breast and Chest

Figure 4-1 is the right breast in a fresh cadaver dissection. For wide exposure of the underlying tissue planes, an incision along the midline of the sternum connects with an incision that parallels the inframammary fold approximately 3 cm below the inframammary fold.

Figure 4-1 Right breast in fresh cadaver specimen. Incision along sternal midline connects to incision 3 cm below inframammary fold (IMF) and parallels the fold.

Dissection in the plane just deep to the deep subcutaneous fascia over the breast exposes the breast parenchymal mass (Figure 4-2) which consists of fatty infiltration of breast tissues with a whiter, fibroglandular tissue connection in the subareolar area. This tissue plane is largely irrelevant in primary breast augmentation unless the surgeon is combining a significant mastopexy procedure with the breast augmentation. When elevating skin flaps off underlying breast tissue, the plane of dissection is critical. Many surgeons, concerned about preserving vascularity to the skin flaps, dissect too deeply, leaving breast parenchyma attached to the skin flaps, when the ideal plane of dissection is immediately deep to the deep subcutaneous fascia. In the correct plane, skin flap elevation preserves optimal suprafascial (to the deep subcutaneous fascia) arterial supply and venous drainage, while minimizing a parenchymal burden deep to the flap that “steals” blood supply from the flaps. Conversely, dissecting excessively superficially when elevating skin flaps compromises critical arterial supply and even more critical venous drainage from skin flaps. The optimal plane of dissection for skin flap elevation, immediately deep to the deep subcutaneous fascia, is well known to surgeons who have performed a large number of mastectomies and to plastic surgeons who must work with the results of these dissections when performing breast reconstruction.

Figure 4-2 Breast parenchymal mass with fatty infiltration of breast tissues (white arrow) and fibroglandular tissue in subareolar area (black arrow).

Reflecting the entire skin, subcutaneous tissue, and breast parenchyma superolaterally exposes the anterior surface of the pectoralis major muscle and the serratus muscle inferolaterally (Figure 4-3). During this dissection, a major objective was to leave pectoralis fascia attached to the anterior surface of the pectoralis major muscle in order to examine the thickness of this fascia in various areas beneath the breast. As a result, remnants of breast parenchyma and fat remain on the anterior surface of the pectoralis major muscle.

Figure 4-3 Breast parenchyma reflected laterally exposes the pectoralis major (black arrow) and serratus anterior (white arrow) muscles.

Medially, the pectoralis major muscle origins arise from the sternum and costal cartilages. While pectoral and clavicular heads of the muscle are defined in anatomy books, these segments are indistinguishable surgically. The relationship of the pectoralis muscle to a breast implant that a surgeon places deep to the muscle is particularly important. While the pectoralis major muscle in this typical cadaver dissection would appear to cover more than three-fourths of a subpectorally placed implant, in the clinical setting the implant tents the pectoralis major anteriorly and the muscle slides medially. If the surgeon leaves all pectoralis major origins intact along the inframammary fold, the muscle covers at most two-thirds of the breast implant intraoperatively, leaving the inferolateral one-third of the implant beneath skin and subcutaneous tissue.

The serratus anterior muscle is located inferolateral to the pectoralis major muscle (Figure 4-3). While some surgeons claim to place implants completely beneath muscle using blunt, blind dissection techniques, elevating the serratus anterior muscle and preserving robust vascularity is challenging under direct vision with wide exposure, and is impossible using blunt, blind dissection techniques. Total muscle coverage, elevating serratus anterior and approximating it to the lateral border of the pectoralis, predictably blunts the inferior and lateral inframammary folds, and is unnecessary and undesirable in primary breast augmentation. The serratus muscle, overlying a breast implant, often suffers vascular compromise and fibrous infiltration over time. The serratus muscle provides unpredictable soft tissue coverage laterally, and often atrophies and blunts delicate lateral and inferolateral breast contours.

Reflecting the pectoralis major muscle superiorly (Figure 4-4) exposes the thoracoacromial pedicle on the deep surface of the pectoralis major muscle, and the pectoralis minor muscle and serratus anterior muscle attached to the chest wall deep to the pectoralis major muscle.

Figure 4-4 Pectoralis major muscle reflected superiorly to reveal pectoralis minor muscle beneath (long white arrow). The thoracoacromial artery (TAA) and pedicle are visible in the fat pad on the deep surface of the pectoralis major (black arrow). The pectoralis minor (long white arrow) and serratus anterior muscles (short white arrow) remain attached to the chest wall deep to the pectoralis major.

Critical Structures in the Subpectoral Tissue Plane

In another fresh cadaver specimen (Figure 4-5), viewing from medially over the sternum, the pectoralis major muscle is reflected laterally to expose structures deep to the pectoralis major. The lateral pectoral nerve courses with the thoracoacromial artery and vein through a fat pad deep to the pectoralis major and into the pectoralis major. The medial pectoral nerve in this specimen exits from deep to the pectoralis minor muscle at its superolateral border and courses anteriorly to innervate the lateral oblique portion of the pectoralis major muscle.

Figure 4-5 Subpectoral plane left breast, viewed from medially. The lateral pectoral nerve and thoracoacromial artery and vein exit the intercostal space and course anteriorly through the fat pad into the pectoralis major. The medial pectoral nerve exits from beneath the superolateral border of the pectoralis minor muscle to innervate the inferior oblique portion of the pectoralis major muscle. Anterior branches of lateral intercostal nerves (black arrows in cadaver photo) exit the intercostal spaces laterally for sensory innervation of the lateral chest and breast.

The location of the medial pectoral nerve can vary, with the nerve sometimes penetrating the pectoralis minor instead of exiting at the lateral border of the muscle. Clinically, the size of this nerve varies considerably. In most cases, surgeons can preserve this nerve when dissecting a subpectoral pocket, but occasionally the nerve exits through the pectoralis minor more inferiorly and can restrict optimal soft tissue redraping over an implant. Division of the medial pectoral nerve, while not optimal, does not produce clinically significant weakness of the pectoralis that causes symptoms in most patients. Laterally, anterior intercostal nerve branches (black arrows) exit the intercostal spaces and course anteriorly to innervate the breast.